1. Technical Field
The present invention relates to an oscillation circuit, an oscillator, a manufacturing method of an oscillator, an electronic device, and a moving object.
2. Related Art
From time to time it is necessary to inspect the characteristics of a vibrator such as a crystal vibrator (piezoelectric vibrator) or a vibrator having a micro electromechanical system (MEMS). To do this, overdrive inspection is performed by inspecting the frequency characteristics of the vibrator by applying an alternating current (AC) signal with high current, voltage, or power to drive the vibrator. Alternatively, drive level inspection may be performed by inspecting the fluctuation of frequency characteristics of the vibrator by applying a signal obtained by gradually increasing or decreasing a frequency of an AC signal with high current, voltage, or power to drive the vibrator.
Recently, however, an oscillator in which a crystal vibrator and an oscillation circuit are accommodated in the same accommodation container (housing) has been developed in order to provide a miniaturized oscillator. Accordingly, various investigations are needed in order to inspect the characteristics of the vibrator after mounting the crystal vibrator and the oscillation circuit in the same accommodation container.
JP-A-2001-102870 discloses a crystal oscillator that includes an analog switch which is controlled by applying a specified DC voltage to an inspecting terminal when inspecting characteristics of a crystal vibrator and a power input terminal. In this oscillator, the crystal vibrator is electrically connected to the inspecting terminal through an analog switch when inspecting the crystal vibrator. On the other hand, the inspecting terminal is separated from the crystal vibrator when normally operating the oscillator.
JP-A-2009-201097 discloses a crystal oscillator which uses a function terminal of the oscillator as an inspecting terminal of a crystal vibrator.
That is, in JP-A-2009-201097, an output terminal and a standby terminal are selected as terminals to be used with the inspecting terminal of the crystal vibrator. This is because a switching circuit is controlled with a power supply voltage when inspecting the characteristics of the crystal vibrator.
To stabilize an operation of the switching circuit, however, it is necessary to apply a potential with high stability to a power supply terminal and a ground terminal. If such terminals are used as the crystal inspection terminal, a signal of the crystal vibrator may be superposed with a DC voltage, and accordingly the power supply voltage may be unstable. Therefore, the two terminals of the crystal vibrator are limited to the output terminal and the standby terminal.
In both JP-A-2001-102870 and JP-A-2009-201097, when inspection of the vibrator is performed, the power supply terminal and the ground terminal are necessary for controlling the analog switch and the switching circuit. In addition, two crystal inspection terminals which are connected to the vibrator are used for the inspection. As such, it is necessary to manage the connection of electrodes and probes electrically connected to the four terminals. Since there are a great number of connection portions to be managed, the likelihood of an inspection malfunction due to a connection failure increases, and the reliability of the inspection may be decreased.